Nitridized ruthenium layer for formation of cobalt interconnects

ABSTRACT

An advanced metal conductor structure is described. An integrated circuit device including a substrate having a dielectric layer is patterned. The pattern includes a set of features in the dielectric for a set of metal conductor structures. An adhesion promoting layer is disposed over the set of features in the patterned dielectric. A nitridized ruthenium layer is disposed over the adhesion promoting layer. A cobalt layer disposed over the nitridized ruthenium layer filling the set of features, wherein the cobalt layer is formed using a physical vapor deposition process.

BACKGROUND OF THE INVENTION

This disclosure relates to integrated circuit devices, and morespecifically, to a method and structure to create advanced metalconductor structures in semiconductor devices.

As the dimensions of modern integrated circuitry in semiconductor chipscontinues to shrink, conventional lithography is increasingly challengedto make smaller and smaller structures. With the reduced size of theintegrated circuit, packaging the circuit features more closely togetherbecomes important as well. By placing features closer to each other, theperformance of the overall integrated circuit is improved.

However, by placing the integrated circuit features closer together,many other problems are created. One of these problems is an increase inthe resistance-capacitance (RC) delay caused at least in part by theincrease in copper resistivity as the dimensions of the features becomesmaller. The RC delay is the delay in signal speed through the circuitas the result of the resistance and capacitance of the circuit elements.

The present disclosure presents improved interconnects to alleviate thisproblem.

BRIEF SUMMARY

According to this disclosure, an advanced metal conductor structure isdescribed. An integrated circuit device including a substrate having adielectric layer is patterned. The pattern includes a set of features inthe dielectric for a set of metal conductor structures. An adhesionpromoting layer is disposed over the set of features in the patterneddielectric. A nitridized ruthenium layer is disposed over the adhesionpromoting layer. A cobalt layer disposed over the nitridized rutheniumlayer filling the set of features, wherein the cobalt layer is formedusing a physical vapor deposition process.

The foregoing has outlined some of the more pertinent features of thedisclosed subject matter. These features should be construed to bemerely illustrative. Many other beneficial results can be attained byapplying the disclosed subject matter in a different manner or bymodifying the invention as will be described.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings which are notnecessarily drawing to scale, and in which:

FIG. 1 is a cross-sectional diagram depicting the dielectric structureafter patterning and etching steps have been performed according to afirst embodiment of the invention;

FIG. 2 is a cross-sectional diagram depicting the substrate structureafter a liner deposition step has been performed according to a firstembodiment of the invention;

FIG. 3 is a cross-sectional diagram depicting the structure after aruthenium (Ru) deposition step has been performed according to a firstembodiment of the invention;

FIG. 4 is a cross-sectional diagram depicting the structure after anitridation step has been performed on the ruthenium (Ru) layeraccording to a first embodiment of the invention;

FIG. 5 is a cross-sectional diagram depicting the structure after acobalt (Co) deposition step has been performed according to a firstembodiment of the invention;

FIG. 6 is a cross-sectional diagram depicting the structure after athermal anneal step has been performed according to a first embodimentof the invention;

FIG. 7 is a cross-sectional diagram depicting the structure after aplanarization step has been performed according to a first embodiment ofthe invention;

FIG. 8 is a cross-sectional diagram depicting the structure after aplanarization step has been performed according to a second embodimentof the invention; and

FIG. 9 is a cross-sectional diagram depicting the structure after aplanarization step has been performed according to a third embodiment ofthe invention.

DETAILED DESCRIPTION OF THE DRAWINGS

At a high level, the invention provides a method and resulting structureto form interconnects which reduce resistance-capacitance (RC) delays ascompared to conventional interconnects. In the invention, ruthenium andcobalt layers are used instead of copper as interconnect materials. Theruthenium/cobalt combination is chosen as cobalt has a better latticematch with ruthenium than alternative materials such as titanium ortantalum. This provides a good interface for performing a reflowprocess. The combination of material provides good metal fill propertiesin aggressively scaled features, e.g., less than twenty nanometers. Withgood metal fill properties, the reliability of the interconnect is alsoimproved.

Although the bulk resistivity value of cobalt is higher than that ofcopper, resistance in thin films and features increases more rapidly inmaterials with a larger mean free path, such as copper, as compared tocobalt (Co). Thus, narrow Co features will display lower resistance thanCu features of comparable size below 30 nm or so. Accordingly, theinventors propose using Co as the bulk conductor in the currentdisclosure vs. Cu used in prior art devices. The lower resistance of Coin small features is expected to show RC delay benefit in narrow wires(<30 nm).

A “substrate” as used herein can comprise any material appropriate forthe given purpose (whether now known or developed in the future) and cancomprise, for example, Si, SiC, SiGe, SiGeC, Ge alloys, GaAs, InAs, InP,other III-V or II-VI compound semiconductors, or organic semiconductorstructures. Insulators can also be used as substrates in embodiments ofthe invention.

For purposes herein, a “semiconductor” is a material or structure thatmay include an implanted impurity that allows the material to sometimesbe conductive and sometimes be a non-conductive, based on electron andhole carrier concentration. As used herein, “implantation processes” cantake any appropriate form (whether now known or developed in the future)and can comprise, for example, ion implantation.

For purposes herein, an “insulator” is a relative term that means amaterial or structure that allows substantially less (<95%) electricalcurrent to flow than does a “conductor.” The dielectrics (insulators)mentioned herein can, for example, be grown from either a dry oxygenambient or steam and then patterned. Alternatively, the dielectricsherein may be formed from any of the many candidate high dielectricconstant (high-k) materials, including but not limited to hafnium oxide,aluminum oxide, silicon nitride, silicon oxynitride, a gate dielectricstack of SiO2 and Si3N4, and metal oxides like tantalum oxide that haverelative dielectric constants above that of SiO2 (above 3.9). Thedielectric can be a combination of two or more of these materials. Thethickness of dielectrics herein may vary contingent upon the requireddevice performance. The conductors mentioned herein can be formed of anyconductive material, such as polycrystalline silicon (polysilicon),amorphous silicon, a combination of amorphous silicon and polysilicon,and polysilicon-germanium, rendered conductive by the presence of asuitable dopant. Alternatively, the conductors herein may be one or moremetals, such as tungsten, hafnium, tantalum, molybdenum, titanium, ornickel, or a metal silicide, any alloys of such metals, and may bedeposited using physical vapor deposition, chemical vapor deposition, orany other technique known in the art.

When patterning any material herein, the material to be patterned can begrown or deposited in any known manner and a patterning layer (such asan organic photoresist aka “resist”) can be formed over the material.The patterning layer (resist) can be exposed to some form of lightradiation (e.g., patterned exposure, laser exposure) provided in a lightexposure pattern, and then the resist is developed using a chemicalagent. This process changes the characteristic of the portion of theresist that was exposed to the light. Then one portion of the resist canbe rinsed off, leaving the other portion of the resist to protect thematerial to be patterned. A material removal process is then performed(e.g., plasma etching) to remove the unprotected portions of thematerial to be patterned. The resist is subsequently removed to leavethe underlying material patterned according to the light exposurepattern.

For purposes herein, “sidewall structures” are structures that arewell-known to those ordinarily skilled in the art and are generallyformed by depositing or growing a conformal insulating layer (such asany of the insulators mentioned above) and then performing a directionaletching process (anisotropic) that etches material from horizontalsurfaces at a greater rate than its removes material from verticalsurfaces, thereby leaving insulating material along the verticalsidewalls of structures. This material left on the vertical sidewalls isreferred to as a sidewall structure. The sidewall structures can be usedas masking structures for further semiconducting processing steps.

Embodiments will be explained below with reference to the accompanyingdrawings.

FIG. 1 is a cross-sectional diagram depicting the dielectric structureafter patterning and etching steps have been performed according to afirst embodiment of the invention. Although only a single damascenefeature 102 is shown for ease in illustration, the patterned dielectricstructure could include a set of vias, a set of trenches, or combinationof the same in different embodiments of the invention. An interconnectformed in via is used to conduct current between the device andconductive line layers, or between conductive line layers. Aninterconnect formed in a trench is part of a conductive line layer whichconducts current parallel to the substrate. As is known, a photoresistor sacrificial mandrel layer can be patterned over a dielectric layer.The subsequent etch will create the dielectric structure depicted inFIG. 1. The dielectric layer 101 is silicon dioxide in preferredembodiments, however, other dielectric materials are used in otherembodiments of the invention. Further, the dielectric layer 101 ispreferably part of a multilayer structure comprising a plurality ofmaterials.

The single damascene structure 102 shown in FIG. 1 has been etched intothe substrate with an aspect ratio (H/D) of height (=H) to width (=D).The example feature shown in FIG. 1 could be a via or a trench. In someembodiments of the invention the range of aspect ratios is 0.5 to 20with aspect ratios of 1 to 10 being preferred. However, in the actualdevice, there may be high aspect ratios (Height/width) which are greaterthan 20:1. A typical range of heights of the patterned structure (ordepths of the patterned structure) H is from 100 nanometers to 10micrometers and a typical range of widths of an individual feature D isfrom 5 nanometers to 1 micrometers.

FIG. 2 is a cross-sectional diagram depicting the substrate structureafter a liner deposition step has been performed according to a firstembodiment of the invention. In preferred embodiments of the invention,a liner material selected from the group of Ta, Ti, W, their nitrides ora combination of the same is deposited. The liner material is depositedas a barrier layer 103 over the patterned dielectric layer 101 utilizingany conventional deposition process including, for example, chemicalvapor deposition (CVD), plasma enhanced chemical vapor deposition(PECVD), physical vapor deposition (PVD) or sputtering. The thickness ofthe layer 103 can vary according to the type of layer being formed andthe technique used in forming the same. Typically, the layer 103 has athickness from 1 nm to 100 nm with a thickness from 2 nm to 20 nm beingmore typical. The liner material 103 prevents the diffusion of thesubsequent RuCo metal layer into the dielectric 101, acting also as anadhesion promoting layer so that the RuCo metal layer is bonded to thesubstrate. Experimental results have shown that direct deposition of Ruon the dielectric produces poor adhesion and causes delamination relatedreliability problems.

FIG. 3 is a cross-sectional diagram depicting the structure after a Rumetal deposition step has been performed according to a first embodimentof the invention. The ruthenium layer 105 can be formed by aconventional deposition process including, for example, chemical vapordeposition (CVD), plasma enhanced chemical vapor deposition (PECVD),atomic layer deposition (ALD), physical vapor deposition (PVD),sputtering, chemical solution deposition and plating. In preferredembodiments, the thickness of the Ru layer will be sufficient to coverthe liner layer 103 and in the range of 1 nm to 100 nm, with a thicknessfrom 2 nm to 20 nm being more typical. As illustrated, the Ru depositionlayer 105 is substantially conformal over the liner layer 103, however,a conformal layer is not a requirement of the invention.

FIG. 4 is a cross-sectional diagram depicting the structure after anitridation step has been performed on the ruthenium (Ru) layeraccording to a first embodiment of the invention. The nitridized Rulayer 107 is created utilizing a plasma or thermal process whichincreases the concentration of nitrogen in at least a surface portion ofthe Ru layer 107. In some embodiments, only a surface layer of rutheniumis converted into a nitrogen enriched layer. In the embodiment asdepicted, the Ru layer 107 is fully nitridized. The thermal nitridationprocess employed in embodiments of the present invention disclosure doesnot include an electrical bias higher than 200 W in anitrogen-containing gas or gas mixture. The nitrogen-containing gasesthat can be employed in the present invention include, but are notlimited to, N2, NH3, NH4, NO, and NHx wherein x is between 0 and 1 ormixtures thereof. In some embodiments, the nitrogen-containing gas isused neat, i.e., non-diluted. In other embodiments, thenitrogen-containing gas can be diluted with an inert gas such as, forexample, He, Ne, Ar and mixtures thereof. In some embodiments, H2 can beused to dilute the nitrogen-containing gas. The nitrogen-containing gasemployed in the present disclosure is typically from 10% to 100%, with anitrogen content within the nitrogen-containing gas from 50% to 80%being more typical. In one embodiment, the thermal nitridation processemployed in the present disclosure is performed at a temperature from50° C. to 450° C. In another embodiment, the thermal nitridation processemployed in the present disclosure is performed at a temperature from100° C. to 300° C. for 30 minutes to 5 hours. In one set of embodiments,the resulting nitride enhanced layer is between 2 angstroms to 30angstroms thick, but alternative embodiments can have thicknessesoutside this range.

In some embodiments, a N2 plasma process is used to create thenitridized layer which involves an electrical bias higher than 350 W. AnN2 plasma can be controlled without damaging the dielectric with ioncurrent density range: 50˜2000 uA/cm2, and process temperature between80 and 350 degrees C. The lattice structures of Ru and Co are close, andwhen the surface of the Ru is nitridized, the overall dimensions of thelattice structure remain. This similarity in lattice structure producesa good Co reflow.

FIG. 5 is a cross-sectional diagram depicting the structure after acobalt (Co) deposition step has been performed according to a firstembodiment of the invention. The cobalt layer 109 is formed by aphysical vapor deposition (PVD) in the preferred embodiment. Depositionof cobalt using other deposition techniques, for example, enhancedatomic layer deposition (ALD), chemical vapor deposition (CVD),sputtering, chemical solution deposition and plating have much greaterimpurities. For example, empirical data indicates that CVD and ALDdepositions have C, Cl, O and S impurities cumulatively in excess of1000 pm while PVD layers have cumulative deposition less than 200 ppm.Test data has indicated that purity of the Co layer 109 is important forcreating a low resistivity conductor. In preferred embodiments, thethickness of the Co layer 109 is at least sufficient to fill the trenchafter a subsequent thermal anneal step. In preferred embodiments, thethickness of the Co layer 109 will be in the range of 2 nm to 800 nm,with a thickness from 5 nm to 100 nm being more typical. Although asillustrated, the Co deposition layer 109 appears substantially conformalover the nitridized Ru layer 107, a PVD deposited film is generally notconformal nor is this a requirement of the invention. The presence ofthe Ru nitride layer 107 improves the reflow properties of the Co inaggressively scaled features (less than 20 nm) and is expected toimprove reliability of the interconnect.

FIG. 6 is a cross-sectional diagram depicting the structure after athermal anneal step has been performed according to a first embodimentof the invention according to an embodiment of the invention. In onepreferred embodiment, the thermal anneal is carried out in a furnacebetween a temperature range between 200-500 degrees Centigrade in aneutral ambient, for example, in an N2, H2, He ambient or a mixturethereof. If carried out in a furnace, the thermal anneal is carried outfor a period of 30 minutes to 5 hours in embodiments of the invention.In another embodiment, the thermal anneal is carried out through laserannealing. 20 nanoseconds to 30 minutes, 400-900 degrees Centigradeusing a similar ambient.

Because of the nitridized layer within the Ru layer 107, either asurface layer or a fully nitridized Ru layer, the Ru layer 107 and theCo layer 109 will remain distinct. Without the nitridized layer at highannealing temperatures, a Ru(Co) alloy would be formed. For a certainthermal platform, a higher annealing temperature requires a shorter timeto complete the reflow process so the nitridized layer is an advantagewhen a separation of the Ru and Co layers should be maintained, but ahigher annealing temperature is desired. Experimental data indicatesthat Co shows a better reflow property on the nitridized Ru surface thanon a pure Ru surface. The thermal anneal also reflows the cobalt 109from the field area into the patterned features in the dielectric due tocapillary driving force.

FIG. 7 is a cross-sectional diagram depicting the structure after aplanarization step has been performed according to a first embodiment ofthe invention. The drawing depicts the structure after a planarizationprocess such as a chemical mechanical polishing (CMP) step has beenperformed according to a first embodiment of the invention. Typically, aCMP process uses an abrasive and corrosive chemical slurry (commonly acolloid) in conjunction with a polishing pad. The pad and wafer arepressed together by a dynamic polishing head and held in place by aplastic retaining ring. As shown, the CMP step has removed the excessportions of the liner layer 103, the nitridized Ru layer 107 and the Colayer 109 in the field areas of the dielectric layer outside thefeatures of the pattern in the dielectric 101. As mentioned above, inembodiments of the invention where a high anneal temperature is used andan Ru(Co) alloy layer formed, the Ru(Co) alloy layer is also removed bythe CMP step. Other planarization processes are known to the art and areused in alternative embodiments of the invention.

FIG. 8 is a cross-sectional diagram depicting the structure after aplanarization step has been performed according to a second embodimentof the invention. This figure corresponds to FIG. 7 which depicts thestructure after a chemical mechanical polishing (CMP) step or otherplanarization has been performed. In FIG. 8, a nitridized layer 111replaces the liner layer 103 of FIG. 3. Like the nitridation of the Rulayer discussed above in the first embodiment, the nitridized layer iscreated utilizing either a plasma or thermal process nitridation processwhich increases the concentration of nitrogen in a surface portion ofthe dielectric 101. Because of the presence of the nitridized layer 109,a liner layer is not required for maintaining adhesion to the nitridizedRu layer 107. That is, Ru layer 107 has good adhesion to the nitridizedlayer 109.

FIG. 12 is a cross-sectional diagram depicting the structure after aplanarization step has been performed according to a third embodiment ofthe invention. The processing is similar to that described above in thefirst and second embodiments, however, in the third embodiment of theinvention, both the enhanced-nitrogen layer 111 and the liner layer 103are used as adhesion promoting layers. Using both layers 111 and 103 ina structure for extra adhesion between the nitridized Ru layer 107 andthe dielectric 101 may be critical for semiconductor products whichrequire high reliability.

In all of the embodiments of the invention discussed herein, thenitridation of the Ru layer, creating a nitridized Ru layer prevents theRu and Co from combining into an alloy and maintains the integrity ofboth layers, even when a high temperature anneal is used.

Processing of additional layers of the integrated circuit deviceproceeds after the steps illustrated in the disclosure. For example, asecond set of conductive lines could be created using an embodiment ofthe invention in subsequent steps if required for completion of theintegrated circuit.

The resulting structure can be included within integrated circuit chips,which can be distributed by the fabricator in wafer form (that is, as asingle wafer that has multiple chips), as a bare die, or in a packagedform. In any case, the chip is then integrated with other chips,discrete circuit elements, and/or other signal processing devices aspart of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboardor other input device, and a central processor.

While only one or a limited number of features are illustrated in thedrawings, those ordinarily skilled in the art would understand that manydifferent types of features could be simultaneously formed with theembodiment herein and the drawings are intended to show simultaneousformation of multiple different types of features. However, the drawingshave been simplified to only show a limited number of features forclarity and to allow the reader to more easily recognize the differentfeatures illustrated. This is not intended to limit the inventionbecause, as would be understood by those ordinarily skilled in the art,the invention is applicable to structures that include many of each typeof feature shown in the drawings.

While the above describes a particular order of operations performed bycertain embodiments of the invention, it should be understood that suchorder is exemplary, as alternative embodiments may perform theoperations in a different order, combine certain operations, overlapcertain operations, or the like. References in the specification to agiven embodiment indicate that the embodiment described may include aparticular feature, structure, or characteristic, but every embodimentmay not necessarily include the particular feature, structure, orcharacteristic.

In addition, terms such as “right”, “left”, “vertical”, “horizontal”,“top”, “bottom”, “upper”, “lower”, “under”, “below”, “underlying”,“over”, “overlying”, “parallel”, “perpendicular”, etc., used herein areunderstood to be relative locations as they are oriented and illustratedin the drawings (unless otherwise indicated). Terms such as “touching”,“on”, “in direct contact”, “abutting”, “directly adjacent to”, etc.,mean that at least one element physically contacts another element(without other elements separating the described elements).

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiment was chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

Having described our invention, what we now claim is as follows:
 1. Anintegrated circuit device comprising: a substrate including a dielectriclayer patterned with a pattern includes a set of features in thedielectric for a set of metal conductor structures; an adhesionpromoting layer disposed on the set of features in the patterneddielectric; a nitridized ruthenium layer disposed on the adhesionpromoting layer; and a cobalt layer disposed on the nitridized rutheniumlayer filling a remainder of the set of features, wherein the cobaltlayer is completely formed using a physical vapor deposition process. 2.The device as recited in claim 1, wherein the adhesion promoting layeris a liner layer.
 3. The device as recited in claim 1, wherein theadhesion promoting layer is a nitrogen enriched layer formed in thepatterned dielectric layer produced by a nitridation process.
 4. Thedevice as recited in claim 1, wherein the adhesion promoting layer iscomprised of a nitrogen enriched layer formed in the patterneddielectric layer produced by a nitridation process and a liner layercomprised of one or more materials selected from the group consisting ofTa, Ti, W, TaN, TiN and WN.
 5. The device as recited in claim 1, whereinthe set of metal conductor structures are a set of conductive lines. 6.The device as recited in claim 1, wherein the metal fill in thedamascene pattern is coplanar with a top surface of the dielectric infield areas of the dielectric layer.
 7. The device as recited in claim1, wherein the set of metal conductor structures are a set of conductivevias.
 8. The device as recited in claim 1, wherein the set of metalconductor structures are a set of conductive lines and vias.
 9. Thedevice as recited in claim 1, wherein a dimension of the set of metalconductor structures is less than 30 nm wherein the overall resistivityof Co is lower than the overall resistivity of Cu so that the RC-delayis reduced.
 10. The device as recited in claim 1, wherein the patterneddielectric structure is a combination of a set of vias and a set oftrenches.
 11. The device as recited in claim 1, wherein a thickness ofthe ruthenium layer is in the range of 2 nm to 20 nm.
 12. The device asrecited in claim 1, wherein the adhesion promoting layer is a nitrogenenriched layer formed in the patterned dielectric layer produced by anitridation process, and wherein an unnitridized portion of theruthenium metal layer is bonded to the nitrogen enriched layer formed inthe patterned dielectric layer.
 13. The device as recited in claim 1,wherein the ruthenium metal layer is a fully nitridized ruthenium layerdisposed on and bonded to the adhesion promoting layer.
 14. The deviceas recited in claim 1, wherein a first dimension of the advancedconnector structure is less than twenty nanometers.